This invention relates to electrostatically-aided atomization and dispensing systems for water-based coating materials and more particularly to systems which are able to mix and dispense both electrically more-conductive coating materials such as water or water-based coating materials, and electrically less-conductive coating materials such as organic solvent and resin-based coating materials. A problem exists when electrostatically-aided atomization and dispensing processes are used to dispense highly conductive coating materials. That problem is isolation of the electrostatic high-potential source from ground.
When applying paint with a hand-held electrostatic spray gun, it is desirable to electrically ground the spray gun body to protect the operator from risk of electrical shock. It is also desirable to electrically ground the paint supply, water supply, and/or solvent resin supply to prevent current from flowing from the paint-charging electrode at the spray gun tip through the paint column to electrically charge the entire paint or water supply. If the paint or water supply is isolated from ground and becomes charged, the operator is at risk of receiving a potentially hazardous shock from the paint or water source as it is replenished or otherwise serviced. It is desirable to protect an operator from electrical shock when the entire paint or water column from the source to the electrostatic spray gun is grounded which minimizes danger of accidents resulting from the rupture, cut or a pin-hole break in the paint supply hose allowing a spark from the paint column to ground. If the paint column were charged and a spark should occur, there is a risk that flammable paint solvents could ignite or explode.
The invention concerns a method for spray coating a product, notably an electrically-conductive coating product such as a water-soluble paint applied electrostatically, and is more particularly concerned with a new arrangement for changing such products rapidly. The invention is more particularly directed to solving the additional problems which arise in this context from electrostatic application of watersoluble paints having a relatively high electric conductivity.
In known conventional installations, the coating-product circuits, compressed-air circuits, and cleaning-product circuits are connected via isolation valves to a manifold having a common outlet branch connected to the electrostatic spray gun. This arrangement will be referred to hereinafter as a "coating-product change unit" or, more simply, a "color change unit." Conventionally, to change color the valve on the circuit of the coating product in use must be closed a particular "computed" time before the end of the current spraying phase and then the compressed air valve opens to propel the remaining product toward the sprayer. The cleaning cycles are then carried out compressing a succession of injections of cleaning product and compressed air until the pipes are clean and dry. Finally, the valve on another coating-product circuit is opened to fill the manifold and the pipes until a little of the new color-coating product exists in the sprayer. A new paint-spraying phase may then begin.